1. Field of the Invention
The present invention relates to photographic cameras, and more particularly to electronic cameras for creating digital images using an electronic image sensor.
2. Description of the Related Art
In conventional photographic film cameras, image recording typically is performed by sequentially projecting optical images onto photographic film. Photons strike light-sensitive chemical grains in the photographic film to form latent images. The latent images are later developed by chemical processing to be viewed directly (as slides) or print on photographic paper.
While conventional photographic camera and film systems produce high-resolution images, such systems do have certain limitations. For example, image storage and retrieval are inconvenient, time-consuming, and it is difficult to copy, to modify, and to transmit the photographic images. Moreover, if the images are to be used with computers or computer networks such as the Internet or Worldwide Web, the images must be scanned or otherwise converted into digital data.
To overcome these and other limitations of conventional film cameras, electronic cameras use an electronic image sensor to capture an optical image and convert the optical image into an electrical image signal. Processing circuits in the electronic camera then convert the electrical image signal into digital data (digital images) suitable for use by a computer or computer network. The digital images can be, stored, transmitted over a network, displayed on a computer display, printed on a computer printer, etc. The digital images can also be easily edited or modified in format, resolution, and color mapping. Special optical effects can also be added.
Unfortunately, many photographers have a significant investment in conventional photographic equipment, that is, photographic equipment designed for photographic film. This investment includes cameras, camera bodies, camera lenses, viewers, viewfinders, flash equipment, and the like. A photographer wishing to switch from conventional film to digital photography (e.g., electronic film (E-film)) is faced with the daunting and expensive task to purchasing new equipment. Moreover, conventional film and E-film tend to be complementary in some respects such that conventional film is better suited to some photographic tasks and E-film is better suited to other photographic tasks. Thus, some photographers choose to use both conventional film and E-film.
The present invention solves these and other problems by providing an electronic film (E-film) apparatus that reversibly converts a conventional film camera body into an E-film camera. The electronic film apparatus includes one or more state sensors that sense the operating state of the camera body without requiring modification or cooperation by the camera body. In one embodiment, the state sensors sense that the camera shutter is about to open, before the shutter actually opens, thereby allowing the imager and associated circuitry to be powered up and initialized prior to the operation of the shutter.
In one embodiment, the state sensors include an electromagnetic sensor. In one embodiment, the state sensors include an acoustic sensor. In one embodiment, the state sensors include an optical sensor. The data gathered by the sensors is used to determine the operating state of the camera. Based on the operating state of the camera, the E-film apparatus operates in various power modes, include very low power modes (e.g. sleep modes), low power modes (e.g. standby modes, digital audio modes), and full power modes (e.g. image acquisition modes). In one embodiment, the E-film apparatus uses data from the state sensors to determine when to initiate image acquisition. In one embodiment, the E-film apparatus uses data from the state sensors to determine when to terminate image acquisition.
In one embodiment, the E-film apparatus includes an E-film cartridge that reversibly converts a conventional 35 mm film camera into an E-film camera. The 35 mm camera can be a single lens reflex (SLR) camera, a point-and-shoot camera, a rangefinder camera, and the like. In one embodiment, the E-film apparatus includes a replaceable camera back that converts a conventional camera, such as a 35 mm camera, medium format cameras, ideal format cameras, large format camera, and the like, into an E-film camera.
In one embodiment, the electromagnetic sensor includes a loop or coil that converts electromagnetic fields into an electrical signal. In one embodiment, the envelope of the electrical signal is detected by an envelope detector. The amplitude of a portion of the envelope is compared to a threshold and, if the envelope exceeds the threshold, the E-film apparatus enters image acquisition mode.
In one embodiment, the acoustic sensor includes a microphone or other vibration sensor that senses vibrations in the camera due to operation of the mechanical aspects of the camera body such as motion of a shutter button, motion of a mirror (as in a SLR camera) and/or motion of a mechanical shutter. The microphone converts vibrations in the camera body into an electrical signal. In one embodiment, the envelope of the electrical signal from the microphone is detected by an envelope detector. The amplitude of a portion of the detected acoustic envelope is compared to a threshold and, if the envelope exceeds the threshold, the E-film apparatus enters an image acquisition mode.
Alternatively, if the amplitude of a portion of the detected acoustic envelope exceeds the threshold, the E-film apparatus enters an acoustic sampling (i.e. digital audio) mode. In the acoustic sampling mode, power is applied to a signal processor (such as a digital signal processor), and the electrical signals from the microphone are provided to an analog-to-digital converter and converted into a string of digital samples. The digital samples are provided to the signal processor. The signal processor computes a frequency spectrum of the digital samples and compares the computed frequency spectrum to an expected frequency spectrum. If the computed frequency spectrum is sufficiently similar to the expected frequency spectrum, then the E-film apparatus provides power to the image sensor and begins image acquisition. In one embodiment, the computed frequency spectrum and the expected frequency spectrum are compared by computing a cross-correlation between the two spectrums.
In one embodiment, the E-film apparatus senses opening of the camera shutter by illuminating the shutter with a light source and measuring the light reflected by the shutter. In one embodiment, the light source is an infrared source. In one embodiment, the infrared source provides short pulses of light and operates at a relatively low duty cycle. In one embodiment, the infrared source is operated only when other sensors, such as the electromagnetic or acoustic sensors have provided data indicating that operation of the shutter appears to be eminent.